Organic geochemistry of the Lower Permian Tak Fa Formation in Phetchabun Province, Thailand: implications for its paleoenvironment and hydrocarbon generation potential

Abstract

The outcrop samples of the Tak Fa Formation (Lower Permian) in Phetchabun Province have been studied to determine their organic geochemical characteristic, depositional paleoenvironment, and hydrocarbon generation potential. The total organic carbon (TOC) values ranging from 1.42 to 4.58 wt% and extractable organic matter values ranging from 76.84 to 197.65 ppm of the Tak Fa Formation were generally low and associated with low S2 values (0.00–0.50 mg HC/g rock) and hydrogen index values in range of 0–32 mg/g TOC, although this could reflect highly thermal maturity and complex tectonic history. Thus, kerogen classification can be based on a non-biomarker study for these outcrop samples instead. The non-biomarker plot, Pr/n-C17 and Ph/n-C18 from this study indicates that organic matter originally comes from type II/III kerogen. The samples were also investigated and indicated that the organic matter inputs were derived from mixed marine and terrigenous sources and deposited under suboxic to oxic conditions. The depositional environment of the Tak Fa Formation in this study is interpreted to be an estuarine environment or restricted lagoonal carbonate platforms. This has been achieved from normal alkane and isoprenoids distributions, terpane, and sterane biomarkers. Thus, the Tak Fa Formation is considered to be a hydrocarbon source rock during the time of the deposition. Although the geochemical data in this study indicate that the Tak Fa Formation has experienced high maturation, one or more locations could meet a condition that places this formation to be an active source rock. The approach and concepts presented in this study can be applied to similar evaporite-carbonate deposits in Thailand to find more petroleum plays.